This invention pertains to rotogravure printing and, more particularly, pertains to a method and apparatus for removing surplus ink from the surface of a rotogravure printing cylinder.
In conventional doctor blade rotogravure printing techniques, ink is delivered in a surplus amount from an ink pot onto the surface of a rotogravure printing cylinder. A doctor blade is provided to strip off from the cylinder surface that surplus ink transferred from the ink pot to the printing cylinder which does not fill out the engraving cells on the cylinder. The doctor blade is typically mounted on a doctor blade holder and the doctor blade is pressed against the cylinder surface under a prescribed angle and under a pressure which can be controlled either in a mechanical or pneumatic fashion. It is known in the prior art to impart to the doctor blade an oscillatory movement in the direction of its working edge, i.e. on a parallel with the cylinder axis. Typically, the frequency of such oscillatory movement imparted to the doctor blade is related to the number of cylinder revolutions in a ratio of, for example, 1:16,666.
Use of a doctor blade as described above which mechanically bears against the surface of the printing cylinder leads to many problems. Thus, wear of the doctor blade and/or the cylinder surface, even in situations where the cylinder surface is provided with a hard chromium coating, occurs. There also occurs uneven wiping off of surplus ink due to non-uniform coordination of the positions of the doctor blade and the cylinder as well as line scratches on the printing cylinder surface due to particles of foreign bodies trapped at the doctor blade wiping edge. The consequences of these above-mentioned irregularities in operation are frequent shutdowns of the printing machine for the purpose of readjustment of the position and of eventual replacement of the doctor blade. Further, there arise problems of maintaining the doctor blade pressure at a desired level and, under given circumstances, inconstancy of tone reproduction of printings by the printing cylinder due to modification of the angular position of the doctor blade and of the geometry of its angle.